Experimental study of irrigation rate, ODC and intrarenal temperature in superpulse fiber thulium laser lithotripsy

The present study aimed to examine the relationship of irrigation velocity, operator duty cycle (ODC), and intrarenal temperature during extracorporeal shockwave lithotripsy with a superpulse fiber thulium laser. Calcium oxalate monohydrate stones were implanted in the renal pelvis of fresh pig kidneys. Puncture technology was used to place a temperature probe accurately in the renal parenchyma about 2 mm away from the stone. To simulate the temperature at which a human body is exposed, that is, 37°C, the experiment was executed in an equilibrated laboratory at a constant temperature of 25°C with 60% humidity. The power of the laser varied between 10W and 30W; that of the irrigation varied from 10 to 30 ml/min. The time that the laser was applied was set at 120 s. Changes in the temperature were recorded online. A direct proportionality of temperature in the kidney to the rate of irrigation has been reported between 10 W and 30 W laser powers. The percentage ratio of the rate of irrigation and power in the laser is 1:1, which can keep the temperature in the kidney at a safe level. More specifically, at a laser power of 20 W and irrigation of 10 ml/min, the temperature inside the kidney increases sharply with the increase in ODC. By decreasing the ratio of ODC, the increase of temperature inside the kidney can be brought to a great reduction. The ratio of laser power to that of irrigation speed should be 1:1; hence, damage or injury to kidney tissue can be efficiently prevented from thermal changes.